Aging behaviour and properties evaluation of high-density polyethylene (HDPE) in heating-oxygen environment

The high-density polyethylene (HDPE) samples aged in heating-oxygen environment were prepared. The mechanical properties were determined by the tensile test and small punch test (SPT), and the chemical properties were determined by Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). Meanwhile, microscopically morphology of tensile fracture was observed successively. The result showed that tensile strength increasing continuously with the aging time increasing; meanwhile elongation and maximum load in SPT reached the maximum value at the aging time of 28 days. The carbonyl index on the sample surface increased significantly with the aging time increasing. At the same time, the molecular weight increased until the aging time is 28 days, and then changed slightly. This means that the aging behaviours based on cross-linking increased firstly, and then degradation played a more important role in materials properties change. The microscopically morphology of tensile test samples could prove this point with the amount of crazes decrease, and the brittleness of aged samples increase.